A prospectus entitled “Bitelli Volpe SF 100 T4M deep-cut cold planer for asphalt and concrete” describes a work machine comprising a frame which is supported by four wheels, a pair of oppositely arranged front wheels and a pair of oppositely arranged rear wheels. One of the rear wheels is adapted to raise and lower the frame relative to the respective rear wheel. Means are provided to allow for two operating positions of the one rear wheel. In a first operating position the rear wheel is mounted at the frame in what is called a projecting position, in a second operating position the rear wheel is mounted at the frame in a retracted position relative to the general outline of the frame. To allow for movement between the two operating positions a support arm is provided, which is, at its one end, pivotally connected to the frame and carries at its other end a wheel support comprising a lifting column. Typically, the rear wheel is driven by a hydraulic motor located in the hub of the rear wheel. Pressurized fluid is supplied to the hydraulic motor (and also any other hydraulic motors of other wheels which need to be driven) from an internal combustion engine mounted to the frame. To move the rear wheel from its projecting position into its retracted position the operator hydraulically lowers the frame with respect to the rear wheel. i.e. a hydraulic cylinder located inside the lifting column provides for this lowering movement. As soon as the frame or some other component fixedly mounted to the frame comes into engagement with the ground, the lifting column is lifted further by means of the hydraulic cylinder, so that the lower surface of the wheel is eventually spaced a certain distance from ground. Preferably, before the lifting of the wheel from ground has occurred, a pin locking the support arm at the frame is removed. After the wheel is spaced from the ground the operator pivots the support arm, and also simultaneously rotates the lifting column so that the running direction of the rear wheel is maintained for the two operating positions.
The possibility of positioning at least one of the rear wheels in the projecting position improves weight distribution during operation of the work machine, while the possibility of positioning the wheel in the retracted position allows the work machine to operate flush to a wall or curb. However, the manual operation of displacing and locking or unlocking the pivotable wheel is somewhat uncomfortable for the operator, who is obliged to leave his seat and carry out the required operations manually.
EP 0 916 004 A1 discloses a work machine for the treatment of roadways having a rear support wheel which can be pivoted between an interior or retracted position and an exterior or projecting position by means of a guide rod gear consisting of a four-link mechanism with four vertical articulated axles and two guide rods pivotable in a horizontal plane connected to the rear support wheel. The guide rod gear pivots the rear wheel supported by a non-rotatingly locked lifting column from the exterior position to the retracted position such that the rear wheel turns in the retracted position and in the exterior position in the same direction. With this design the respective load of the work machine resting on the rear wheel is distributed to all four links of the four-link mechanism, which may result in a reduced stability and stiffness of the work machine. Also, precise couplings have to be provided which need to be inspected frequently so as to keep the wear, which might compromise good operation of the work machine, under control.
Further, typical cold planers may be fitted with tracks instead of wheels which is of advantage especially for very heavy machines. As with wheels, it is desirable to be able to change the relative position of at least one of the tracks relative to the frame, i.e. in a retracted or projecting position relative to the frame. However, this also changes the steering characteristic for the whole machine which is more accentuated when the machine is fitted with tracks instead of wheels.
The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.